The spring coefficient of a conventional helical spring is made according to a predetermined specification before the spring is produced, so it is usually not available to be used in various mechanisms. Thus, a special spring that is adjustable is provided, but the cost of development and manufacturing is high.
To improve what is mentioned above, an invention of Taiwan Patent No. 436588, titled “Adjustable Casing for Helical Spring”, was disclosed. The device includes male and female cases and a rotation member, characterized in that two ends of a helical spring are respectively mounted to a fixed base in the center of the bottom of the female case and to the inside of the male case. A plurality of resists of the outer or inner bore of the rotation member contact the coil of spring, and thus the rotation member is rotated to change the number of compressed coils of the helical spring that receives a compressive force or tension, thereby the spring coefficient of the helical spring is adjusted. However, the adjustable helical spring mentioned above, especially the helical spring of large diameter, when actually used, results in various problems.
In consideration of the mentioned-above defects of the prior art, this inventor provide this invention having reasonable and effective improvements of the defects of the conventional structures mentioned above.